This invention relates to internal cooling within a gas turbine engine, and more particularly, to an apparatus and a method for providing better and more uniform cooling in a transition or interface region between a combustor liner and a transition piece.
Traditional gas turbine combustors use diffusion (i.e., non-premixed) combustion in which fuel and air enter the combustion chamber separately. The process of mixing and burning produces flame temperatures exceeding 3900° F. Since conventional combustors and/or transition pieces are generally capable of withstanding a maximum temperature on the order of only about 1500° F. for about ten thousand hours (10,000 hrs.), steps to protect the combustor and/or transition piece must be taken. This has typically been done by film-cooling which involves introducing relatively cool compressor air into a plenum formed by an impingement cooling sleeve surrounding the transition piece and a flow sleeve surrounding the combustor liner. This cooling air is ultimately reverse-flowed into the combustor where it mixes with fuel for combustion and dilution tuning.
Various techniques have been employed to cool the aft end of the combustor liner (that end adjacent the transition piece) and the compression seal (or “hula” seal) typically used at the interface of the transition piece and combustor liner. See, for example, U.S. Pat. No. 6,098,397 which discloses providing an array of concavities on the outside surface of the liner to enhance heat transfer. Another technique is disclosed in U.S. Pat. No. 7,010,921 where the aft end of the combustor liner is provided with a plurality of axially extending ribs or turbulators about its circumference, covered with a sleeve or cover plate, thus forming a series of cooling channels. Cooling air is introduced into the channels through air inlet slots or openings at the forward end of the channels, and exits into the transition piece which is telescoped over the aft end of the liner.
Tuning of the combustor (including the cooling configuration), which can only be done after the turbine is operational, typically involves disassembly of the turbine and removal of the transition piece for drilling or welding dilution holes therein. This is a time-consuming and thus costly process.
There remains a need, therefore, for a cooling arrangement that provides effective, uniform cooling of the aft end of the combustor liner/transition piece interface, but that also simplifies the combustor tuning process.